The long-range goal of this project is to determine the mechanism used by bacteria to select the proper cell division site at midcell. The three Min proteins, MinC, MinD and MinE, are required for proper site selection. The proteins have a unique cellular localization pattern and undergo a unique pole-to-pole oscillatory cycle. We have recently shown that the MinCDE proteins are organized into spiral filaments that wind around the cell between the two poles in a cytoskeletal-like structure that appears distinct from a coiled structure formed by the MreB protein. During the proposed grant period we will use a combination of fluorescence microscopy, biochemistry and genetics to achieve the following aims: i. Min protein structure and function-- To determine the effects of mutations that interfere with the topological specificity function of the MinCDE system, ii. Long-range organization of the Min system-- To define the organization of the MinDE cytoskeletal-like elements within the cell, to determine whether the Min and MreB spiral filaments are separate structures, to characterize proteins that interact with MinD and MinE, and to determine whether there is a relationship between the Min spiral filaments and chromosome segregation, iii. MreB-- To isolate the MreB and Min cytoskeletal-like structures, to characterize proteins that interact with MreB, and to define the behavior of the MreB cytoskeletal-like structures during the course of the cell cycle.